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1.7.0 CONTROL STORAGE
Control storage on the basic System/32 consists of
4K addressable positions. On machines with the
Control Storage Increment feature, control storage
contains 8K addressable positions. Because'the
additional 4K word increment of control storage
does not directly affect hardware operations, it
is not discussed in further detail.
Control storage contains part of the system con-
trol program and microroutines to process the
system instructions. The illustration shows the
areas where the microroutines reside after they
are loaded into control storage from the disk.
The system emulator classifies system instruc-
tions as processing unit instructions or as
input/output instructions. When the system
instruction is classified as a processing unit in-
struction, the emulator also executes the instruc-
tion. If the system instruction is classified by
the emulator as an input/output instruction, it
is executed by the appropriate I/O area of con-
trol storage.
After the emulator classifies a system instruction
as an I/O instruction for one of the devices, con-
trol is passed to the appropriate area of control
storage. For example, a disk instruction is
exe-
cuted by the disk I/O area of control storage,
printer instructions by the printer I/O area, and
keyboard and display screen instructions by the
keyboard/CRT I/O area.
The I/O interrupt handler processes micro
interrupts.
The keyboard decode table in the keyboard/CRT
I/O area translates the data bits coming from the
keyboard into a standard code. The CRT buffer
in this area assembles the message for the display
screen. This buffer is then transferred to the
buffer in the display attachment. If the message
is to be printed, the printer takes the information
from the CRT buffer.
The transient area is used for devices whose micro-
routines are not loaded into control storage at
IMPL. For example, the 33FD microroutines are
loaded from the disk into the transient area of
control storage when that device is called.
The nucleus functions area is used with the
system control program.
The direct area and fixed communications area
contain system registers, machine check log, and
interrupt branch tables. These areas are common
areas used by all the microroutines.
Control Storage
Direct Area
Fixed Communications Area
Reserved for Optional Features
:
--
Keyboard Decode Table/CRT Buffer
System Emulator
Disk I/O
Printer I/O
Keyboard/CRT I/O
I/O Interrupt Handler
Transient Area
--
Nucleus Functions
Control Storage Increment (4K Words)
Communications Area
ECS Supervisor
Available Area
Introduction
1-7
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